The Mars Express recently made some historically close passes to Mars' moon, Phobos, and managed to snap some detailed close-up shots. These are the closest views of the rock we've seen... or is it a rock?

The Mars Express flybys, which happen every five months, may also determine if Phobos is a fragile pile of rocky fragments stuck together — what planetary scientists refer to as a rubble pile — or solid through and through.

Some of the new images taken March 7 during one of several recent close flybys of the moon home in on the proposed landing site for a Russian mission, Phobos-Grunt (meaning Phobos soil), that is expected to touch down on the moon next year.